Idiopathic scoliosis is a relatively prevalent and serious orthopedic disability. It is characterized by a lateral curvature associated with rotation of the vertebra and by a hereditary tendency. The pathogenesis of this disorder is yet to be determined. In our investigations of idiopathic scoliosis, bioengineering technology was applied to examine behavioral observations of dysequilibrium (most pronounced with visual feedback coupled with perturbed body motion) and of visual-vestibular ocular instability (evidenced by asymmetry and by lack of suppression of the vestibulo-ocular reflexes). These observations were attributed to abnormal physiological functioning of certain brain stem and cerebellar processes with particular emphasis upon vestibular activity. We concluded that these biological and behavioral outcomes were directly associated with the structural deformity; there was no evidence that the abnormal curvature had an indirect or secondary effect upon our findings. The intended goal of this project is to pursue further the casual relationship between brain stem functioning and structural asymmetry in children with idiopathic scoliosis. The proposal aims to study the natural history of the disability by evaluating the outcomes (visual-vestibular and curvature) of two specific groups of "high risk," skeletally immature subjects, namely female subjects with curves between 11 degrees and 25 degrees (Group I) and "normal" siblings of children with idiopathic scoliosis (Group II). Stimulus-response characteristics (symmetry, gain, and phase) of visual and vestibular generated eye movements under various conditions of stimulation are determined in both normal subjects and in Group I and II subjects of comparable ages. Data is analyzed (1) to compare normal with high risk subjects and degree and type of spinal curvature with various imposed test conditions; and (2) to correlate clinical-radiographic and behavioral data to predict progression of the curve in Group I or occurrence of a substantial curvature (beyond 10 degrees) in Group II. If the prediction model supports the etiological hypothesis, it is conceivable that principles of contemporary management will be markedly altered, leading to simpler techniques of therapy and, conceivably, to prevention of the disorder.